A boojum seed harvesting adventure

Gonzalo called me over and said, “Hey, check this out.” He had lashed a cardboard box onto a thick saguaro rib with some bailing twine. It looked like what you would use to lower a stranded cat out of a tree, should the cat be so bold—or stupid—to step into the box.

“Becky and I are going to harvest some boojum seeds. She’ll cut and I’ll catch.”

The target plant was our newest and second largest boojum tree. It was acquired from a boojum grower in Tucson and transplanted to the Arboretum last November. It has done exceeding well in its new location, potentially producing a boxful of seeds—or so we were about to find out.

The slope was steep, with decomposed rhyolite as loose and hazardous to walk on as a patina of frozen peas. Becky wielded a long, telescoping pole pruner, and Gonzalo used his pole to position the box under each cluster as she snipped. The conversation had a lot to do with where the fruits would fall. “Which side is the gravity?” Gonzalo asked. I wanted to answer, All sides, I but I knew that wouldn’t be helpful. The tree had a slight bend near the top and it wasn’t immediately evident where the cut fruit cluster would fall.

“I think I can reach it from down here,” Becky answered. She made her way down slope and Gonzalo moved towards the opposite side, almost falling when his right foot slipped on the gravely rhyolite along the side slope. He caught himself by stabbing the end of the saguaro rib against the rock, nearly sloshing out some of the hundreds of fruits that were loosely piled in the box.

Becky was now assuming the telltale posture of an archer, but rather than drawing a bow string, she was grasping the rope that would close the steel jaws of the lopper on the targeted fruit cluster. “Don’t cut back too far,” Gonzalo advised, “just enough to get the fruits at the end.” He stood at a ninety degree angle to her position and placed the box directly under her loppers. A big part of this process was just staying out of each others way.

“Ready?” she asked. It was a rhetorical question, one that she had asked a dozen times already. We couldn’t hear the fruits go plunk into the box when she snipped, but if none hit the ground, it was a successful catch.

This sequence, with minor variations, was repeated over and over, so the system had become routine. At one point, though, I heard Gonzalo yell, “Becky, freeze! Don’t move!” I looked out from my camera, expecting to see a six-inch centipede crawling up her leg, but he was pointing to a dozen stray fruits that had somehow fallen on her shoulder. “We need them all,” he said. I had done nothing but watch up to this point, so I plucked them off her shoulder one-by-one, placing them in the box that he had lowered and held in front of me.

The entire process took less than an hour. As interesting as this was to watch, these weren’t the first boojum seeds they had harvested this year, just the highest. We now have over twenty-five boojum trees of various ages in the Arboretum collection, and about a half dozen are mature enough that staff have collected viable seeds from them in each in the past two years.

Gonzalo separated the seeds from the hulls (the fruits) and allowed the seeds to dry before putting them in a vermin-proof glass bottle. His preferred method for planting the seeds is to clump-flat them in shallow rectangular trays filled with fine sand. The seeds germinate in about ten days without any pre-treatment and produce an impressive 5” tap root in just a few months after germination. One of the seedlings planted in November 2013 is already an inch and a half tall with a quarter inch thick stem. This little precocious upstart is the exception, though, not the rule. The baby boojums will be bumped up into progressively into larger containers over the coming years until they reach a size where they have the best chance of survival on the grounds.

The prime harvest time is late September through mid-October, though seeds have been harvested as late as November. The earlier harvest time yields a better success rate because less opportunity is given to predators, both insects and birds, to beat us to the punch.